On 2/1/2022 4:22 pm, Jietao Xiao wrote:
Qemu-kvm will create several kernel threads for each VM including
kvm-nx-lpage-re, vhost, and so on. Both of them properly inherit
the cgroups of the calling process,so they are easy to attach to
the VMM process's cgroups.
Kubernetes has a feature Pod Overhead for accounting for the resources
consumed by the Pod infrastructure(e.g overhead brought by qemu-kvm),
and sandbox container runtime usually creates a sandbox or sandbox
overhead cgroup for this feature. By just simply adding the runtime or
the VMM process to the sandbox's cgroup, vhost and kvm-nx-lpage-re thread
can successfully attach to the sanbox's cgroup but kvm-pit thread cannot.
Emm, it seems to be true for kvm-pit kthread.
Besides, in some scenarios, kvm-pit thread can bring some CPU overhead.
So it's better to let the kvm-pit inherit the cgroups of the calling
userspace process.
As a side note, there is about ~3% overhead in the firecracker scenario.
By queuing the attach cgroup work as the first work after the creation
of the kvm-pit worker thread, the worker thread can successfully attach
to the callings process's cgroups.
Signed-off-by: Jietao Xiao <shawtao1125@xxxxxxxxx>
---
arch/x86/kvm/i8254.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 0b65a764ed3a..c8dcfd6a9ed4 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -34,6 +34,7 @@
#include <linux/kvm_host.h>
#include <linux/slab.h>
+#include <linux/cgroup.h>
#include "ioapic.h"
#include "irq.h"
@@ -647,6 +648,32 @@ static void pit_mask_notifer(struct kvm_irq_mask_notifier *kimn, bool mask)
kvm_pit_reset_reinject(pit);
}
+struct pit_attach_cgroups_struct {
+ struct kthread_work work;
+ struct task_struct *owner;
+ int ret;
+};
+
+static void pit_attach_cgroups_work(struct kthread_work *work)
+{
+ struct pit_attach_cgroups_struct *attach;
+
+ attach = container_of(work, struct pit_attach_cgroups_struct, work);
+ attach->ret = cgroup_attach_task_all(attach->owner, current);
This cgroup_v1 interface is also called by the vhost_attach_cgroups_work(),
as well as the kvm_vm_worker_thread() in the KVM context.
This part of the code may be a bit redundant as the number of kthreads increases.
+}
+
+
+static int pit_attach_cgroups(struct kvm_pit *pit)
+{
+ struct pit_attach_cgroups_struct attach;
+
+ attach.owner = current;
+ kthread_init_work(&attach.work, pit_attach_cgroups_work);
+ kthread_queue_work(pit->worker, &attach.work);
+ kthread_flush_work(&attach.work);
+ return attach.ret;
+}
+
static const struct kvm_io_device_ops pit_dev_ops = {
.read = pit_ioport_read,
.write = pit_ioport_write,
@@ -683,6 +710,10 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
if (IS_ERR(pit->worker))
goto fail_kthread;
I wonder if we could unify the kthread_create method for both vhost and kvm-pit
so that all kthreds from kvm_arch_vm agent could share the cgroup_attach_task_all()
code base and more stuff like set_user_nice().
+ ret = pit_attach_cgroups(pit);
+ if (ret < 0)
+ goto fail_attach_cgroups;
+
kthread_init_work(&pit->expired, pit_do_work);
pit->kvm = kvm;
@@ -723,6 +754,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
fail_register_pit:
mutex_unlock(&kvm->slots_lock);
kvm_pit_set_reinject(pit, false);
+fail_attach_cgroups:
kthread_destroy_worker(pit->worker);
If it fails, could we keep it at least alive and functional ?
fail_kthread:
kvm_free_irq_source_id(kvm, pit->irq_source_id);
